The very high temperatures and pressures in Jupiter's core mean scientists cannot tell what materials would be there. This cannot be found out, because it is not possible to create the same amount of pressure on Earth.

Above the unknown inner core is an outer core. The outer core of Jupiter is thick, liquid hydrogen.[21] The pressure is high enough to make the hydrogen solid, but then it melts because of the heat.

Jupiter is twice as massive as all the other planets in the Solar System put together.[13] It gives off more heat than it gets from the sun.[22] Jupiter is 11 times the width of Earth and 318 times as massive. The volume of Jupiter is 1,317 times the volume of Earth. In other words, 1,317 Earth-sized objects could fit inside it.[23]

Most of the clouds on Jupiter are made of ammonia.[26] There may also be clouds of water vapour like clouds on Earth. Spacecrafts such as Voyager 1 have seen lightning on the surface of the planet. Scientists think it was water vapour because lightning needs water vapour.[27] These lightning bolts have been measured as up 1,000 times as powerful as those on Earth.[27] The brown and orange colours are caused when sunlight passes through or refracts with the many gases in the atmosphere.

One of the biggest features in Jupiter's atmosphere is the Great Red Spot. It is a huge storm which is bigger than the entire Earth. It is on record since at least 1831, [28] and as early as 1665.[29][30] Images by the Hubble Space Telescope have shown as many as two "red spots" adjacent to the Great Red Spot.[31][32] Storms can last for hours or as long as hundreds of years in the case of the Great Red Spot.[33][34]

Jupiter has a magnetic field like Earth's but 11 times stronger.[35] It also has a magnetosphere much bigger and stronger than Earth's. The field traps radiation belts much stronger than Earth's Van Allen radiation belts, strong enough to endanger any spacecraft travelling past or to Jupiter. The magnetic field is probably caused by the large amounts of liquid metallichydrogen in the core of Jupiter.[36] The four largest moons of Jupiter and many of the smaller ones orbit or go around the planet within the magnetic field. This protects them from the solar wind. Jupiter's magnetic field is so large, it reaches the orbit of Saturn 7.7 million miles (12 million km) away.[37] The Earth's magnetosphere does not even cover its moon, less than a quarter of a million miles (400,000 km) away.

Jupiter also has a thin planetary ring system.[38] These rings are difficult to see and were not discovered until 1979 by NASA's Voyager 1 probe.[39] There are four parts to Jupiter's rings. The closest ring to Jupiter is called the Halo Ring.[40] The next ring is called the Main Ring. It is about 6,440 km (4,002 mi) wide and only 30 km (19 mi) thick.[40] The Main and Halo rings of Jupiter are made of small, dark particles.[39] The third and fourth rings, called the Gossamer Rings, are transparent (see through) and are made from microscopic debris and dust.[39] This dust probably comes from small meteors striking the surface of Jupiter's moons. The third ring is called the Amalthea Gossamer Ring, named after moon Amalthea. The outer ring, the Thebe Gossamer Ring, is named after the moon Thebe. The outer edge of this ring is about 220,000 km (136,702 mi) from Jupiter.[40]

The orbit of a planet is the time and path it takes to go around the Sun. In the amount of time it takes for Jupiter to orbit the Sun one time, the Earth orbits the Sun 11.86 times.[41] One year on Jupiter is equal to 11.86 years on Earth. The average distance between Jupiter and the Sun is 778 million kilometres. This is five times the distance between Earth and the Sun. Jupiter is not tilted on its axis as much as the Earth or Mars. This causes it to have no seasons, for example Summer or Winter. Jupiter rotates, or spins around very quickly.[42] This causes the planet to bulge in the middle. Jupiter is the fastest spinning planet in the Solar System.[42] It completes one rotation or spin in 10 hours.[12] Because of the bulge, the length of the equator of Jupiter is much longer than the length from pole to pole.[43]

The Pioneer missions were the first spacecraft to take close up pictures of Jupiter and its moons. Five years later, the two Voyager spacecraft discovered over 20 new moons. They captured photoevidence of lightning on the night side of Jupiter.[47]

The Ulysses probe was sent to study the Sun. It only went to Jupiter after it had finished its main mission. Ulysses had no cameras so it took no photographs. In 2006, the Cassini spacecraft, on its way to Saturn, took some very good, very clear pictures of the planet. Cassini also found a moon and took a picture of it but it was too far away to show the details.[48]

The Galileo mission in 1995 was the first spacecraft to go into orbit around Jupiter. It flew around the planet for seven years and studied the four biggest moons. It launched a probe into the planet to get information about Jupiter's atmosphere. The probe travelled to a depth of about 150 km before it was crushed by the weight of all the gas above it.[49] This is called pressure. The Galileo spacecraft was also crushed in 2003 when NASAsteered the craft into the planet. They did this so that the craft could not crash into Europa, a moon which scientists think might have life.[49]

NASA have sent another spacecraft to Jupiter called Juno. It was launched on August 5, 2011.[50] The spacecraft arrived at Jupiter on July 4, 2016.[51] Several missions have been planned to send spacecraft to Jupiter's moonsEuropa and Callisto. One called JIMO (Jupiter Icy Moons Orbiter) was cancelled in 2006 because it cost too much money.[52]

Jupiter has 69 known moons.[4] The four largest were seen by Galileo with his primitive telescope, and nine more can be seen from Earth with modern telescopes. The rest of the moons have been identified by spacecraft.[53] The smallest moon (S/2003 J 12) is only one kilometre across. The largest, Ganymede, has a diameter of 5,262 kilometres. It is bigger than the planet Mercury.[54] The other three Galilean moons are Io, Europa and Callisto. Because of the way they orbit Jupiter, gravity affects three of these moons greatly. The friction caused by the gravity of Europa and Ganymede pulling on Io makes it the most volcanic object in the Solar System. It has over 400 volcanoes, more than three times as many as Earth.[55]

A diagram of the inner Solar System. It shows the two groups of Trojan asteroids that follow Jupiter in its orbit

Jupiter's large gravity has had a big effect on the Solar System. Jupiter protects the inner planets from comets by pulling them towards itself. Because of this, Jupiter has the most comet impacts in the Solar System.[46]

Two groups of asteroids, called Trojan asteroids, have settled into Jupiter's orbit round the Sun. One group is called the Trojans and the other group is called the Greeks. They go around the Sun at the same time as Jupiter.[56][57]

↑Stuart Ross Taylor (2001). Solar system evolution: a new perspective : an inquiry into the chemical composition, origin, and evolution of the solar system (2nd, illus., revised ed.). Cambridge University Press. p. 208. ISBN0-521-64130-6.